Chapter 12

Question 1

What is the shape of alkanes?

Answer 1

Each C atom surrounded by 4 sigma bonds - atoms can freely rotate around sigma bond
Electron pairs repel as far apart as possible so 3D shape = tetrahedral 109.5

Question 2

What is the bonding in alkane?

Answer 2

Each C atom is joined to 4 other atoms by single covalent bonds = sigma bond (overlap of atomic orbitals directly between bonding atoms)

Question 3

What are the boiling points of alkanes?

Answer 3

C1-C4 = gases
C5-C16 = liquids
C17+ = solids

Effect of the chain length: as chain length increases, SA increases = more surface contact = greater London forces
Effect of branching: fewer surface contact points = weaker London forces

Question 4

What are the limitations of radical substitution reactions?

Answer 4

Further substitution: in propagation another Br radical could attack to form a diloalkane, continues until all 4 atoms have been substituted

Question 5

What are the combustion reactions of alkanes?

Answer 5

With plentiful O2 = produces H2O and CO2
Without plentiful O2 = produces H2O and CO or C

Question 6

What is the reactivity of alkanes?

Answer 6

Lack of reactivity = crude oil deposits
C-C and C-H sigma bonds are strong
C-C bonds are non-polar
C and H have close electronegativity = non-polar

Question 7

What happens in the reaction between alkanes and halogens?

Answer 7

Requires presence of UV sunlight
Observations: bromine is decolourised, moist litmus paper turns red = substitution reaction

Question 8

What are the steps for halogenation?

Answer 8

1, Initiation (formation of radicles requires UV) Br-Br —> Br. + Br.

2. Propagation: C5H12+Br. —> C5H11. + HBr AND C5H11+Br2 —> C5H11Br + Br.
3. Termination: Radicals collide